Pendulum valves are particularly useful in high purity gas delivery systems, such as those used in semiconductor manufacturing or other thin film coating processes. The valves are particularly useful for processes performed at very low pressures (high vacuums), e.g., a pressure on the order of one torr or less. One ultra-high vacuum system adapted to operate at low conductances includes a turbo pump, and a pendulum or slide valve for controlling the pressure created by the turbo pump within a predetermined range. Such systems typically utilize a turbo pump and a combination of valves connected together so as to provide a closed system as well as careful control of pressure when the pendulum valve is near the closed and sealed position, where pressure control is more difficult.
As the dimensions of semiconductor devices decrease and their densities increase, semiconductor manufacturing processes have become increasingly dependent on precise pressure and mass flow control. It is thus critical that the valve body of the pendulum valve make a tight seal with the valve seat when the valve is moved to its closed position. The movement of the valve body of a pendulum valve, usually in the form of a disk, is between a completely opened position and a completely closed position. The movement usually requires rotational movement between a first angular position and a second angular position, and some translational movement so that the disk can be moved into alignment with the opening in the valve and so that the disk can be moved into contact with a valve seat provided around the inside edge of the opening through which gas flows. Prior pendulum valves typically use multiple actuator elements which are inherently difficult to effect precise movement of the valve body of the pendulum valve, and therefore more difficult to utilize for flow control purposes. For examples of such prior pendulum valves see the following: U.S. Pat. Nos. 2,850,260; 3,557,822; 3,722,857; 3,973,753; 4,052,036; 4,089,505; 4,333,631; 4,627,567; 4,785,844; 5,577,707; 5,873,562; British Patent No. 1,050,435 and German Patent 1,190,755. Other valve structures are shown in U.S. Pat. Nos. 2,749,082; 3,854,696; 4,073,468; 4,088,301; 4,135,854; 4,395,049; 4,442,996; 4,458,905; 4,519,578; 4,921,213; 5,379,983; 5,330,157;